Testing device for ignition systems



Jan. 18, 1944. M. P. MccAR-rv y 2,339,713

TESTING DEVICE 'FOR IGNITION SYSTEMS Filed May l2, 1941 invention, shown as Patented Jan. 18, 1944 UNITED STATES PATENT oFFlcE.

' TESTING DE'YICE FOR lIGrNIllONv SYSTEMS Madison P. McCarty, Dallas, Tex., assignmof one-half to John B. Donovan, Dallas, Tex.

Application May 12, 1,941, Serial No. 393,039

2 Claims. (Cl. 17E-183) This invention relates to testing devices for the ignition system of internal combustion engines and it has particular reference to apparatus effective to -visibly indicate the condition of the spark plugs, condenser and other electrical 'units in the ignition Circuit.

The principal object of the invention is to provide an instrument comprised of an electric crcuit including a choke coil and resistance in series with a neon tube, the arrangement being such that the behavior of the tube will afford a visual indicationof the resistance at the spark gap, that is to say, the variance in electrical resistance at the spark gap of an engine spark plug, due to compression differentials, 'will become immediately apparent for correction.

' Another and equally important object of the c invention is to provide an instrument of the character set forth which when connected across the breaker points, in multiple with the condenser of the system, will disclose the Y condition of the condenser. n the other hand,

Systems in 381118 is obvious. Moreover. the in strument employs a s-lled tube of a low striking voltage preferably of the anode-cathode typewhich utilizes the discharge or stored-up ple withv the interrupter points of a conventional engine ignition system. and

Figure 2 is a schematic wiring diagram of a slightly modied form of the invention.

Electrical apparatus for visually determining the operative condition of electrical systems wherein electrically excitable gas-nlled tubesl are employed are, of course, well known. However,

the behavior of the tubes in such apparatus range -from erratic illumination-to a steady, intermittentglow to' indicate deficiencies or defectiveness of the units of'a system such as poor breaker point contacts. weak battery and the like. The present invention accomplishes, through the me- ,dium of a cathode-anode type of electronic discharge tube, a more definite observation of the behavior of the system under test by reason of the illuminative gradient reected on the elec-` trodes. deiciencies of the system being revealed by the degrees of illumination on the anode while the illumination on the cathode indicates proper performance of all oi `the units of the system. However, in cases where the faults in a system under test are of a serious nature, or where the capacity of the condenser of such system is to be determined, the cathode itself will reilect these conditions. For example, the anode of the tube Y will indicate, by reason of back-up current from eneirgyfromthecondenser-inthesystermtocfthe invention enables tests to be made on the Yroadandintheairwellasinservicestations With the foregoing objects as paramount. the invention has further objects to accomplish which a novel structure is provided, an

ment being illustrated in the w drawingwherein:

Flgurelisaschematicwirlng is in proper ratio. In addition to these objects,

conn in muitithe condenser, varying resistances at the sparkplug gaps. due to variances in compression. On the other hand, the cathode denitely shows by varying degrees of illumination the relative capac- A proper or defective contacts between the interruptefncints. l

Continuing with a more detailed description of the drawing', Figure 1 illustrates a conventional ignition systeme: an internal combustion engine. wherein is provided the coil lo having the usual'primarywinding i! andsecondary winding i2. The secondary winding is connected to the center post i3 by 'wire lt. The distributor rotor l5 es successively the contacts ES which are in tum connected to the spark plugs li h wires i8. The secondary win is grounded at i9 through circuit ofbattery te. whichinturnisded at2t.

ff winding li ofthe tion coil is connectedbymeans ofwireitothebreaker l), whose' contact 24 engages the stationary breaker point 278, grounded at 2l. The conventi cam 25 actuatesthe breaker arm 2a. The

condenser 2l is connected .across the brer tsandisdedatzl.

crease the sensitivity of the tester to govern they effectiveness of the illumination of the electrodes.

In operation, with the wires 3B and connected in multiple across the condenser 21 of the conventional ignition circuit, as shown, discharge of the condenser through the primary winding I I, this current being directlyopposite to the flow of current to battery 20 demagnetizes the iron core of the ignition coil and thus produces an extremely high electromotive force in the secondary winding `I2 of the coil. First, the electromotive force of self-induction establishes the current that charges the condenser. When the condenser discharges at the opening of the breaker points, the voltage of discharge is sufciently high to overcome the opposing electromotive force of the battery and to force an instantaneous current through the primary winding Il of the ignition coil and the battery 20, against the resistance of these parts.

This current reduces the magnetism of the core of the ignition coil to zeroalmost instantaneously, thus Aproducing the maximum induction in the secondary coil I'2. The condenser dis-A charges current or voltage when all factorsin the system are in proper working order, and eects ionization of the gases and illuminates the cathode or negative electrode of the tube 28. So long as the system remains `in good operating condition, the cathode or negative electrode remains fully illuminated.

Any resistance set upin the primary circuit such as may be due to faulty breaker point contacts, low battery voltage, defects in the coil and the like will cause a fall in the illuminative gradient of the cathode electrode, the degree or intensity of the glow varying in accordance with applied voltage or general condition of this circuit. The reason for the behaviorfof the cathode as described is due to restriction of current ow through the primary Il of the coil set up by resistance caused by improper breaker point con- 'tact,.shorted turns in the primary winding and like defects. Self-inductance charging the condenser being reduced by these resistances and other factors restricts .the amount of current Aflowing to the condenser 21 and this directly versedirection through the primary of the coil and since the ,current flow through the primary of the coill is effected by the current being taken off the secondary of the transformerfthe condition of the secondary circuit thereby aifects the primary current in the coil by varying the curis charged and immediately discharges in a reresistance of spark pluggaps aected by the gap setting, also by the cleanliness of insulator surfaces or the compression .of cylinder, which also aiects the resistance across spark plug gaps. All have a modifying effect on the amount of current which flows from the secondary of transformer thereby varying the. amount of current flowing in the primary of the transformer or coil.

If this variation in the primary current is of suflicient magnitude, the anode 33 of tube 28 is also illuminated and such illumination takes place also due to faulty conditions in the primary circuit connected to primary of coil as well as those inthe secondary.

'The cause of this anode illumination is due to the fact that when defects in either the primary or secondary circuits are sufciently severe to cause the collapsing effect of the ux in the core of the transformer torbe slow, the condenser 21 receives a charge back in the opposite direction from which it originally discharged through primary ll when the breaker 23 opened. 'I'his reverse charge into the condenser represents one of the iirst few oscillations of the condenser charge and discharge which is known to be of oscillatory nature, the voltage of the successive charges and discharges decreasing as the oscillations proceed. It is obvious from the foregoing that the peculiar` behavior of one or the other or both of the electrodes of the tube provide a definite indication to one skilled in the art as to the perfomance or lack of performance of an ignition system as well as a signal as to what factor in the system is faulty to render the same ineifective.

In Figure 2 is shown a modified form of the circuit illustrated in Figure l, although the same type of tube 31 is employed having anode-cathode electrodes, as shown.

In this form of the invention, the circuit 38, containing the choke 39, resistance 40 and tube 31, is connected in multiple across the points of the interruptor 4l, with theresistor 42 connected in multiple therewith. The anode of tube 31 is connected to a movable contact arm 43 by means of which the amount of resistance shunted across tube 31 may be variedat will. The value of this variable resistance is to adjust or balance the voltage across tube 31 in accordance with the characteristics of the various ignition systems or circuits to which .the device may be connected for testing purposes. The behavior of the tube 31 is substantially the same as in the preceding case, that is, the electrodes vary in illuminativeintensity or gradient depending upon the nature ofthe defect inthe ignition circuit. 'I'he movable contact arm 48` serves the same purpose in the modified circuit aitthe condenser 3l in the first described circ The function of the choke coil 38 is to limit undesirable radio frequencies and the resistance I is to introduce sufficient resistance in the circuit so the forced oscillations are reduced in the tube circuit. as in the preceding case.

Manifestly, the construction as shown and described is capable of some modification and such modification as may be construed to fall within the scope and meaning of the appended claims is also considered to be within the spirit and intent of the invention.

What is' claimed is:

1. In an apparatus for testing'the ignition circuit of internal combustion engines, a tube cirrent taken from the secondary. Therefore, the cuit arranged to be cgnnegd with the prima circuit of said ignition circuit, a tube containing electrically excitable gases and having anode and cathode electrodes jointly and individually illuminated upon ionization of said gases by electronic action set up in said tube by the action of said ignition circuit, the intensity and gradient of said illumination on either oi' said electrodes being determined by the fluctuations of current ow in said ignition circuit anci a condenser in the primary of said ignition circuit 10 whose oscillatory discharge excites the gases of said tube, a variable condenser in parallel with said tube for controlling said oscillatory discharge, and resistance means in said tube circuit for limiting undesirable radio frequencies l5 and to introduce into said tube circuit a resist-V ance to reduce forced oscillations therein.

2. In an apparatus for testing the emciency of the elements of the ignition system of an intemal combustion engine, an anode-cathode tube, 

